I think I saw kleinbl00 mention in the other thread that this feature would have the potential to turn PMing into "invite only subreddits" or something of the sort. Though I kind of figure that can be done now if people wanted to do so. So the question is, would being able to use hubwheels in PMs really hurt?

2) Should the OP be able to add more people to the PM? This is currently possible.

I like the whole functionality of being able to do mass PMs. I think as long as the PM OP is the only one who can add people to the discussion, I don't see a problem with it. I think if anyone in the PM chain can add anyone though, then we might start getting into the territory of "invite only subreddits."

At the heart of any ranking aggregator, however, is the ranking. Currently, there is no ranking within the PM system, therefore putting it somewhat aside and parallel to core aggregator functionality.

By adding ranking to PMs, they become directly competitive with the core functionality - the same, in fact, only with added echo-chambery goodness.

And that's my real problem: Hubski is already a bit of an echo chamber just because the size and community tends to attract like. Most of us are pretty good folx. A "shadow Hubski" could be the absolute opposite of that, and considering hubski's sterling moral character, I suspect very little snooping would happen. But we can't even really test that because there aren't enough nasty shits about to truly see what a wretched den of scum and villainy could be created.

Can anyone add anyone else to a PM conversation? Can anyone remove anyone else? How does blocking/muting/hushing work within a PM? My concern is not that this is a good or a bad thing, my concern is that this is a complex thing with difficult-to-map consequences and that none of us will really have a handle on what it does until it has irrevocably shaped Hubski.

I think as long as the PM OP is the only one who can add people to the discussion, I don't see a problem with it.

It hasn't been a problem yet that I am aware of. It can be very useful. However, it is probably best that everyone knows that the OP can do this. Imagine I am telling thenewgreen how I wish b_b would shower after his hockey nights, and then thenewgreen invites him into the PM.